IN ANGIOSPERMAE. XEROPHILOUS PLANTS 167 



lamina is reduced until the form of the phyllode is attained. In some 

 species foliage-leaves may again appear after the phyllodes, for instance in 

 Acacia heterophylla. 



2. The features of Eucalyptus recall in some degree those of Acacia. 

 In Eucalyptus there are no phyllodes on the older plants, but pendant 

 leaves with a knife-blade-form and showing similar structure on both 

 sides are distributed over the axis of the shoot. The seedling on the 

 other hand forms oval dorsiventral opposite and decussate leaves for 

 a long time on its four-angled twigs. The two stages of development 

 have thus an entirely different aspect. 



3. Many dicotyledonous plants exhibit much the same phenomena 

 as those I have depicted in the case of many Cupressineae l . Some New 

 Zealand species of Veronica, such as V. cupressoides and V. lycopodioides, 

 show in quite a striking manner the habit of the Cupressineae with scale- 

 like adpressed leaves. The seedlings of these species, so far as they are 

 known, all have spreading leaves which possess a stalk and blade like 

 those of other species of Veronica ; but this differentiation disappears in 

 the leaves which appear later. We may assume a similar behaviour for 

 Melaleuca micromera, a cypress-like myrtaceous plant, on account of the 

 phenomena of reversion 2 it exhibits. Passerina hirsuta 3 also has in its 

 young condition spreading leaves whilst the subsequent ones are ad- 

 pressed ; other species of Passerina however only possess the spreading 

 leaf corresponding with the juvenile form of P. hirsuta. 



4. Plants in which the adult leaves are arrested : 



Zilla myagroides, a cruciferous plant possessing shoot-axes containing 

 chlorophyll and constructed as thorns, has only arrested leaves, whilst 

 in its juvenile stage there are large well-developed leaves 4 . 



Clematis afoliata exhibits a gradual reduction of the leaves upon 

 the seedling plants and the newly formed shoots. 



Carmichaelia stricta possesses flattened shoot-axes with arrested leaves 

 but shoots which proceed from its base behave as does the seedling plant. 

 There appears upon the seedling plant after the cotyledons a simple 

 undivided primary leaf just as in other Leguminosae which have been 

 already referred to ; following this comes a trifoliate leaf, and next a few 

 imparipinnate leaves with two to three pairs of pinnules, and then the 

 formation returns either to a trifoliate leaf or to a simple one, and 

 higher up on the flat stem the leaves are reduced to small scales. The 

 formation of leaves attains in the pinnate foliage-leaves its highest point 

 and then again sinks. The conformity of the primary leaves with those 

 reduced ones which appear after the pinnate foliage-leaves shows very 



1 See page 154. ! See page 172. 



' See the figure by Pasquale in Plate i of his book 'Sulla eterofillia.' Napoli, 1867. 



* Goebel, Pflanzenbiologische Schilderungen, i. Fig. 3, 



